This invention relates to liquid level transducers and quality sensors, and more particularly to a liquid level transducer with a removable sensor module for determining the quality as well as other properties of the liquid being measured independent of liquid level determination.
Transducers for measuring liquid level are often used in vehicles, industrial equipment, as well as other mobile and stationary systems and components. The electrical output of such transducers varies in response to a change in the liquid level being measured and is typically in the form of a change in resistance, capacitance, current flow, magnetic field, and frequency. These types of transducers may include variable capacitors or resistors, optical components, Hall Effect sensors, strain gauges, ultrasonic devices, reed switch arrays, and so on.
In vehicles, industrial equipment and other systems powered by diesel fuel, a Selective Catalytic Reduction (SCR) system has been used to inject urea—a liquid-reductant agent—through a catalyst into the exhaust stream of a diesel engine. Urea sets off a chemical reaction that converts nitrogen oxides in the exhaust into nitrogen and water, which is then harmlessly expelled through the vehicle tailpipe. Previous urea quality sensor solutions have attempted to address industry quality control by ensuring that a specific quality of urea can be delivered into the exhaust gas stream. If the engine is operated without urea solution in the onboard urea tank, excessive NOx emissions can occur. Using a urea quality sensor, the SCR system can monitor the contents of the urea tank to alert an operator and/or system that the urea tank has been filled with other fluids, e.g., with tap water, coolant, windshield wiper fluid, oil, incorrect concentrations of urea solutions, and so on, instead of the correct concentration of urea solution. The introduction of a urea quality sensor into the SCR system also reduces the risk of tampering or accidental mis-filling and helps ensure compliance to environmental legislation, thus satisfying concerns of users and legislators alike. The urea quality sensor is intended to contribute to the overall success of SCR as a NOx reduction technology.
Besides monitoring the quality of DEF within the tank, the level of liquid in the tank must also be monitored to ensure that the DEF solution does not run out during operation. Accordingly, liquid level transducers have been used in conjunction with a quality sensor to determine both the level and the quality of the liquid within the tank. However, environmental regulations and/or the development and deployment of industry standards relating to diesel exhaust emissions have been largely unenforceable due at least in part to the lack of identifying a quality sensor that can meet the desired rigid standards. Consequently, many manufacturers of diesel-powered equipment provide DEF tanks with only a liquid level transducer, having opted to forego the added expense of providing quality detection solutions of the fluid within such tanks. When industry- or government-imposed standards are approved and enforcement of such standards becomes practical, DEF quality sensors may be required for both OEM and after-market applications. Under such conditions, prior art solutions do not provide built-in flexibility to retro-fit existing liquid level transducers with quality sensors. Accordingly, the manufacturer or end user may be faced with the expense of replacing a working liquid level transducer with a device that can detect both the liquid level and the quality of the fluid in the DEF tank, especially where the installation of in-line quality detectors may not be practical.
It would therefore be desirable to provide a liquid level transducer that can easily be upgraded to receive one or more interchangeable sensor modules for determining various properties of the fluid being measured. It would also be desirable to provide interchangeable modules that have different features or purposes dependent on or independent of the quality of liquid level within a tank.